The invention relates to techniques for electronically varying the partitioning of planar arrays or phase scanned arrays into sub-arrays or subapertures.
In many airborne radar modes, in particular the terrain following and terrain avoidance modes, difference patterns stabilized with respect to the horizon are required. The technique generally used to generate sum and difference patterns in gimballed planar arrays or phased scanned arrays is to partition the array into quadrants with a separate output for each quadrant. The appropriate quadrant outputs are summed or differenced to provide a sum pattern and two difference patterns. The two difference patterns provide tracking error signals referenced to the antenna.
Conventional solutions to the problem of providing roll stabilized sum and difference patterns in airborne radars include providing a third gimbal or implementing rather cumbersome and not entirely satisfactory signal processing to derive roll stabilized tracking outputs. The roll gimbal technique is probably not feasible for active array systems of sufficient size to require liquid cooling. An alternative to the signal processing approach is needed.
It would therefore represent an advance in the art to provide an active array which can be electronically roll stabilized without the need for mechanical roll gimbals or cumbersome signal processing.
It would further be advantageous to provide a multifunction active array which may be electronically configured into a plurality of arbitrary sub-arrays or subapertures.